1. Field of the Invention
The present invention relates to a liquid discharging method, a liquid discharge head, and a liquid discharge apparatus which discharge a desired liquid using bubbles formed by acting thermal energy on the liquid. The present invention relates especially to a liquid discharging method, a liquid discharge head, and a liquid discharge apparatus which use a movable member relying on bubbles in moving.
The present invention can be used for printers which make records on recording media made of paper, threads, fibers, fabric, leather, metal, plastic, glass, wood, ceramics, etc.; copying machines; fax machines with a communications system; word processors with a printer; and industrial recorders which are combined with various equipment.
In this specification, the term xe2x80x9crecordingxe2x80x9d means to print not only a meaningful image, such as a letter or a figure, but a meaningless image, such as a pattern, on a recording medium.
2. Related Background Art
An ink jet recording method, a so-called bubble jet recording method, is known which forms an image by ejecting ink through a discharge port against a recording medium using a force caused by an ink state change due to energy, such as heat, given to ink, which change is accompanied by a rapid volume change (bubble formation). As disclosed in U.S. Pat. No. 4,723,129, a recorder using such a method commonly has a discharge port through which ink is discharged, an ink flow path which communicates with the discharge port, and an electricity-heat converter which is means for generating energy for discharging ink disposed in the path.
Such a recording method allows a high-quality image to be formed fast with low noise. In addition, because a head using such a method allows ink mainly discharge ports to be densely disposed, an image with high resolution and furthermore a color image can easily be provided by a small apparatus. For these reasons, the bubble jet recording method has recently been used for a variety of office equipment, including printers, copying machines, fax machines, and even industrial systems, such as textile printing machines.
Such a liquid discharge head is known which has a movable member and a stopper. Like a cantilever, the movable member is supported on a bearing upstream of a heating element (opposite to a discharge port), and the free end of the member is positioned downstream of the element (on the discharge port side). In contact with the movable member, the stopper substantially closes the upper part of an ink flow path when the movable member moves as bubbles grow.
In the liquid discharge head, the movable member moves, coming into substantial contact with the stopper to substantially close the upper part of the ink flow path when the heating element produces bubbles. Thus, energy generated by bubbling is used efficiently for ink discharge.
Immediately after a bubble grows to a maximum size and then starts to shrink, the upper part of the ink flow path remains substantially closed, so that ink mainly flows from the discharge port toward the bubble (upstream). Thus ink droplets are rapidly separated from ink in the liquid discharge head and discharged properly.
As the bubble shrinks, an ink flow and the inertia of the movable member cause the member to move to a position where the member opens the ink flow path more widely than when it is in the normal position. Because of this, the flow resistance of the upper part of the ink flow path temporarily decreases to a great extent, so that the head can rapidly be refilled with ink.
When the movable member returns to the normal position finally, the resistance of the upper part of the ink flow path becomes relatively, thus restricting an ink refilling flow. Thus a meniscus formed due to the inertia of the flow can be prevented from moving downstream to excess and vibrating.
As described above, a liquid discharge head with a movable member and a stopper can discharge ink at short time intervals and be driven at a high frequency because the head can rapidly be refilled with ink without meniscus vibration.
Japanese Patent Application Laid-Open No. 2000-62181 and No. 2000-62183 and the like disclose the relationship between the operating condition of a movable member and discharge timing which allows ink to be discharged properly, which relationship is observed when a liquid discharge head is driven at a high frequency. That is, these documents say that providing the next ink discharge when a movable member is in a specific operating condition inhibits ink droplets from being divided into main droplets and auxiliary droplets (satellites) and allows bubbling energy to be efficiently used for ink discharge.
However, the relationship between the behavior and position of a meniscus, which is closely related to record quality, and discharge timing has not yet been disclosed clearly.
It is an object of the present invention to provide a liquid discharge head which can be driven properly at high speed, a liquid discharging method, and a liquid discharge apparatus by appropriately specifying the relationship between the behavior and position of a meniscus and discharge timing, the structure of an ink flow path, and especially the relationship between the path and orifice plate thickness.
To attain the objective, a liquid discharge head according to the present invention having a heating element which heats liquid in a liquid flow path to produce a bubble in liquid; a discharge port through which liquid is discharged by pressure involved in bubble growth, the discharge port communicating with the lower part of the liquid flow path and being smaller in the area of a cross section at right angles to the direction of liquid introduction than the liquid flow path; a movable member which is provided like a cantilever in the liquid flow path, the free end of the member being positioned on the side of the discharge port; and a restrictor which substantially closes the upper part of the liquid flow path by being substantially brought into contact with the movable member when the movable member is displaced by the growth of the bubble, wherein a meniscus is in the discharge port when due to bubble breakage, the movable member moves from the normal position in such a direction that the liquid flow path is open widely and then returns to the normal position.
When the movable member moves from the normal position to the side of the heating element due to bubble breakage, a liquid discharge head, which has a movable member and a restrictor, is rapidly refilled with liquid, so that a liquid meniscus dashes back to the discharge port. When the meniscus does so, the orifice plate and nozzle may shift with respect to each other due to workmanship variations, or a liquid flow may not be uniform on a cross section at right angles to the direction of liquid introduction, depending on the position of the restrictor or movable member, so that the meniscus inclines. If the next liquid discharge is performed with the meniscus inclined, the direction of liquid discharge drifts, thus degrading a recorded image.
The inventors found that if the meniscus goes back into the discharge port, the effect of the inclination of the meniscus is substantially eliminated. This is due to the fact that the inclination of the meniscus in the discharge port is negligible because of the relatively small area of that cross section of the discharge port which is at right angles to the direction of liquid introduction. Thus if a liquid discharge head is designed so that the movable member moves from the normal position to the heating element side for the meniscus to go back into the discharge port while the head is refilled with liquid relatively fast, the next liquid discharge can properly be performed immediately after refilling, and liquid can be sequentially discharged at short time intervals.
A liquid discharge head according to the present invention is further adapted so that when liquid is discharged, the position of the meniscus significantly varies and that then the rate of positional variation sharply decreases, starting at a certain position when the meniscus is in the discharge port. It is desirable that the liquid discharge head have means for controlling the heating element and that the means controls the heating element so that the next liquid discharge is performed by the time that the meniscus reaches the liquid discharge surface after the rate of positional variation sharply changes.
A liquid discharge apparatus according to the present invention includes such a liquid discharge head as described above and recording medium conveying means for conveying a recording medium which receives liquid discharged from the liquid discharge head.
A liquid discharge apparatus according to the present invention can preferably be used for an apparatus which makes records by discharging liquid from a liquid discharge head to attach ink to a recording medium.
A liquid discharging method according to the present invention, comprising the steps of producing a bubble in liquid by heating it, moving a cantilever-like movable member in the path from the normal position as the bubble grows, substantially closing the upper part of a liquid flow path when the bubble attains the maximum volume, discharging liquid through a discharge port which is smaller in the area of a cross section at right angles to the direction of liquid introduction than the liquid flow path, and returning the movable member to the normal position when the bubble breaks after liquid is discharged, wherein a meniscus is in the discharge port when the movable member returns to the normal position after the member moves from the normal position to the heating element side due to bubble breakage, and the next liquid discharge is performed during the period from the time when the movable member returns to the normal position to the time when the meniscus reaches the liquid discharge surface.
A liquid discharging method according to the present invention is still further adapted so that when liquid is discharged, the position of the meniscus significantly varies, that then the rate of positional variation sharply decreases, starting at a certain position when the meniscus is in the discharge port, and that the next liquid discharge is performed by the time that the meniscus reaches the liquid discharge surface after the rate of positional variation sharply changes.